Adhesive sheet and process for manufacturing electronic part

ABSTRACT

An adhesive sheet comprising a sheetlike base material and, superimposed on one major surface thereof, an adhesive layer, wherein the average surface roughness on one major surface of the base material is in the range of 0.1 to 3.5 μm and on the other major surface thereof is in the range of 0.05 to 0.7 μm. In this structure, the average surface roughness values on both the major surfaces of the base material as a constituent of the adhesive sheet are regulated so as to fall within respective specified ranges, so that not only can any blocking occurring in backwinding of reeled adhesive sheet be inhibited but also any occurrence of minute unevenness (waving) on the wafer surface after grinding can be inhibited, and further that the transparency of the adhesive sheet can be maintained.

TECHNICAL FIELD

The present invention relates to an adhesive sheet and a process formanufacturing an electronic part.

BACKGROUND ART

Due to recent advances in the performance of electronic devices such ascellular mobile telephones, the importance of grinding techniques hasbecome broadly recognized. An adhesive agent that is able to firmlysecure a work piece without transferring any foreign particles of asubmicron order to the work piece when the agent is peeled off isdesired in grinding processes. One of the known methods for securing awork piece is to use an adhesive sheet (see Patent Documents 1-3).

During the manufacture of an electronic part, an electronic partassembly forming a circuit pattern on a semiconductor wafer made ofsilicon or gallium-arsenide and the like, or an electronic part assemblyforming a circuit pattern on a tabular insulating substrate and the likeis often used. Moreover, with advances in the functional performance ofelectronic devices, various materials such as Si, SiO₂, Si₃N₄, AlSi,AlSiCu and PI have come to be used on the circuit patterns onsemi-conductor wafers.

Patent Document 1: JP-B H06-018190

Patent Document 2: JP-A 2000-008010

Patent Document 3: Japanese Patent No. 3729584

DISCLOSURE OF THE INVENTION Problems to be Solved by the Invention

However, the conventional art described in the above documents has roomfor improvement with regard to the following points.

First of all, back-grinding, which is characterized by securing thecircuit side of an electronic part assembly to an adhesive sheet andgrinding the back side of the circuit, is a popularly employed grindingprocess. However, when a conventional adhesive sheet is used inback-grinding, blocking tends to occur when unwinding the rolledadhesive sheet, and in some cases, the grinding process (back-grinding)further results in minute irregularities (waving) on the wafer surface.

Secondly, some users leave the protective sheet (adhesive sheet) intactand check the surface circuit patterns and lots through the tape. Thereis thus also a need for the protective sheet (adhesive sheet) to betransparent.

The present invention was conceived in view of the above circumstances,with the object of providing an adhesive sheet that can reduce blockingincidences during the unwinding of a rolled adhesive sheet, suppressoccurrences of minute irregularities (waving) on ground wafer surfaces,and further has transparency. Additionally, another object of thepresent invention is to provide a process for manufacturing anelectronic part using the adhesive sheet.

Means for Solving the Problems

The present invention provides an adhesive sheet comprising a sheet-likebase material and an adhesive layer laminated on one surface of the basematerial, wherein the average surface roughness of one surface of thebase material is at least 0.1 μm and at most 3.5 μm and the averagesurface roughness of the other surface of the base material is at least0.05 μm and at most 0.7 μm.

This constitution allows the average surface roughness of both surfacesof the base material constituting the adhesive sheet to be adjustedwithin their respective specified ranges, thereby enabling the presentinvention to reduce blocking incidences during the unwinding of therolled adhesive sheet, suppress occurrences of minute irregularities(waving) on ground wafer surfaces, and further maintain the transparencyof the adhesive sheet.

Moreover, the present invention provides a process for manufacturing anelectronic part, wherein the electronic part is obtained by grinding awafer, comprising a step of applying a wafer to the adhesive layersurface of the adhesive sheet, and a step of grinding the exposed wafersurface smooth.

This process allows the average surface roughness of both surfaces ofthe base material constituting the adhesive sheet to be adjusted withintheir respective specified ranges, thereby enabling the presentinvention to reduce blocking incidences during the unwinding of theadhesive sheet, suppress occurrences of minute irregularities (waving)on the ground wafer surface, and further maintain the transparency ofthe adhesive sheet.

EFFECTS OF THE INVENTION

The present invention allows blocking incidences during the unwinding ofan adhesive sheet to be reduced, occurrences of minute irregularities(waving) on ground wafer surfaces to be suppressed, and the transparencyof the adhesive sheet to be maintained.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 A section view showing the steps in the back-grinding process ofa wafer using an adhesive sheet.

FIG. 2 A section view showing how blocking occurs during the winding andunwinding of an adhesive tape.

-   -   101 Silicon wafer    -   102 Vacuum chuck table    -   103 Adhesive layer    -   104 Release film    -   105 Release liner    -   106 Base material film    -   108 Rolled adhesive sheet with a release liner    -   110 Adhesive sheet

BEST MODES FOR CARRYING OUT THE INVENTION

Herebelow, modes for carrying out the invention shall be explained withreference to the drawings. Since the same symbols are used to indicatethe same structural components throughout the figures, explanations areomitted where it is appropriate.

DESCRIPTION OF TERMINOLOGY

In the present specification, a monomeric unit refers to aconstitutional unit derived from a monomer. Parts and % in the presentinvention are by mass unless specifically indicated otherwise.

BRIEF OVERVIEW OF THE EMBODIMENTS

FIG. 1 is a section view showing the steps in the back-grinding processof a wafer using an adhesive sheet. As shown in FIG. 1( a), an adhesivesheet 110 of the present embodiment comprises a base material 106 and anadhesive layer 103 laminated on one surface of base material 106.

With the average surface roughness of both surfaces of base material 106constituting adhesive sheet 110 adjusted within the respective specifiedranges, blocking incidences during unwinding of the rolled adhesivesheet 110 can be reduced, occurrences of minute irregularities (waving)on ground wafer surfaces can be suppressed, and the transparency of theadhesive sheet can further be maintained.

<Base Material>

For adhesive sheet 110 of the present embodiment, the average surfaceroughness (Ra1) of one surface (the surface coated with the adhesive) ofthe sheet-like base material 106 is preferably 0.1 μm or above, and isparticularly preferred to be 1.0 μm or above. Keeping the averagesurface roughness (Ra1) above these lower bounds allows blockingincidences between base material 106 to be reduced when only basematerial 106, which constitutes adhesive sheet 110, is wound. On theother hand, this average surface roughness (Ra1) is preferably 3.5 μm orbelow, and is particularly preferred to be 3.0 μm or below. Keeping theaverage surface roughness (Ra1) below these upper bounds allows thetransparency to be maintained and further allows occurrences of minuteirregularities (waving) on the ground surface of semiconductor wafer 101to be suppressed.

Moreover, in adhesive sheet 110 of the present embodiment, the averagesurface roughness (Ra2) of the other surface (the surface not coatedwith the adhesive) of sheet-like base material 106 is not particularlyrestricted as long as it is within a range that does not cause blocking.Specifically, it is preferably 0.05 μm or above and is particularlypreferred to be 0.1 μm or above. Keeping this average surface roughness(Ra2) above these lower bounds allows blocking between base material 106to be reduced when only base material 106, which constitutes adhesivesheet 110, is wound. On the other hand, this average surface roughness(Ra2) is preferably 0.7 μm or below, and is particularly preferred to be0.4 μm or below. Keeping the average surface roughness (Ra1) below theseupper bounds allows the transparency to be maintained, and furtherallows occurrences of minute irregularities (waving) on the groundsurface of semiconductor wafer 101 to be suppressed.

For adhesive sheet 110 of the present embodiment, the stiffness ofsheet-like base material 106 can be easily adjusted by using EVA(ethylene vinyl acetate). In other words, at least a part of sheet-likebase material 106 preferably comprises ethylene vinyl acetate.Particularly, when an adhesive sheet is used in the grinding ofsemiconductor wafer 101 and the base material is too soft, themechanical impact from the grinding head (not shown in drawings) resultsin the vertical motion of semiconductor wafer 101 and the wafer cannotbe ground to an even thickness. Moreover, when sheet-like base material106 is formed of multiple layers, at least one layer among the multiplelayers should preferably comprise EVA (ethylene vinyl acetate). Since atleast one layer of the multiple layers comprises EVA (ethylene vinylacetate), this constitution also allows easy adjustment of thestiffness.

In order to adjust for the flexibility, the vinyl acetate content in theEVA (ethylene vinyl acetate) is preferably 3% or above by mass, and ismore preferably 5% or above by mass. When the vinyl acetate content isabove these lower bounds, the stress exerted during grinding can beabsorbed, and therefore cracks in the ground semiconductor wafer 101 canbe suppressed. On the other hand, in order to adjust for theflexibility, the vinyl acetate content in the EVA (ethylene vinylacetate) is preferably 20% or below by mass, and is more preferably 15%or below by mass. When the vinyl acetate content is below these upperbounds, the degree of grinding precision of semiconductor wafer 101 canbe improved.

For adhesive sheet 110 of the present embodiment, sheet-like basematerial 106 does not need to comprise only EVA (ethylene vinylacetate); it may further comprise multiple materials. Methods employingmultiple materials include methods that use mixtures, co-polymers,laminated films and the like.

For adhesive sheet 110 of the present embodiment, the thickness ofsheet-like material 106 is not particularly restricted; however, toensure the strength and to maintain the flexibility of adhesive sheet110, the thickness is preferably at least 10 μm and at most 300 μm.

<Adhesive Layer>

For adhesive sheet 110 of the present embodiment, the adhesive used foradhesive layer 103 may contain acrylic polymers that allow easyengineering of the adhesive strength and curing agents that enable moreprecise adjustments of the adhesive strength. Moreover, at least one ofthe acrylic monomers constituting the acrylic polymers preferablycontains a functional group-containing monomer. The functionalgroup-containing monomer is preferably mixed and polymerized to have aconcentration that is at least 0.01% and at most 10% of the acrylicpolymers by mass. If the proportion of the functional group-containingmonomer is 0.01% or above by mass, the adhesive strength towards theadherend is strong enough that water penetration tends to be suppressed.If the proportion of the functional group-containing monomer is 10% andbelow by mass, the adhesive strength to the adherend is not too strongand adhesive residues tend to be reduced.

Examples of the main monomers in the acrylic polymers include acrylicmonomers such as butyl (meth)acrylate, 2-butyl (meth)acrylate, t-butyl(meth)acrylate, pentyl (meth)acrylate, octyl (meth)acrylate,2-ethylhexyl (meth)acrylate, nonyl (meth)acrylate, decyl (meth)acrylate,lauryl (meth)acrylate, methyl (meth)acrylate, ethyl (meth)acrylate,isopropyl (meth)acrylate, tridecyl (meth)acrylate, myristyl(meth)acrylate, cetyl (meth)acrylate, stearyl (meth)acrylate, cyclohexyl(meth)acrylate, and benzyl (meth)acrylate.

It is especially preferable for a part of these acrylic monomers to befunctional group-containing monomers. The functional group-containingmonomers are preferably monomers with a functional group such as ahydroxyl group, a carboxyl group, an epoxy group, an amide group, anamino group, a methylol group, a sulfonate group, a sulfamate group or aphosphate (phosphite) ester group. Among the monomers, vinyl compoundshaving the above functional groups are particularly preferred, and vinylcompounds having a hydroxyl group are further preferred. Additionally,the vinyl compounds described here include the acrylates describedbelow.

Examples of the functional group-containing monomers having a hydroxylgroup include 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl(meth)acrylate, and 2-hydroxybutyl (meth)acrylate.

Moreover, adhesive layer 103 of the present embodiment, after the aboveacrylic polymers are allowed to read with a curing agent to cureadhesive layer 103, preferably comprises a carboxyl group-containingmonomers, which constitutes the acrylic polymers, at 1% or below of theacrylic polymers by mass. In other words, among the functionalgroup-containing monomers in the adhesive that have been reacted with acuring agent, the functional group-containing monomer having a carboxylgroup is preferably present at 1% or below by mass. Since the use of afunctional group-containing monomer having a carboxyl group increasesthe adhesive strength towards metals, when the functionalgroup-containing monomer having a carboxyl group is above 1% by massafter its reaction with a curing agent, the adhesive strength towardsmetals is so strong that it tends to leave adhesive residues. It istherefore better to keep the monomer at 1% or below by mass. For thisreason, the carboxyl group-containing monomer is preferably one easilydegradable by a reaction with a curing agent. For example, (meth)acrylicacid, crotonic acid, maleic acid, maleic anhydride, itaconic acid,fumaric acid, N-(glycolic acid)acrylamide and cinnamic acid arepreferably used.

For adhesive sheet 110 of the present embodiment, the adhesive used foradhesive layer 103 is preferably prepared with curing agents. Whencuring agents are included, the ratio is preferably at least 0.1 partand at most 20 parts of the curing agent by mass per 100 parts of theacrylic polymers by mass. When the ratio of the curing agent is at least0.1 and at most 20 parts by mass, adhesive residues can be reduced.

The curing agents used for adhesive layer 103 may be polyfunctionalisocyanate curing agents, polyfunctional epoxy curing agents, azirinecompounds, melamine compounds and the like, and are more preferablypolyfunctional isocyanate curing agents or polyfunctional epoxy curingagents. By using polyfunctional epoxy curing agents or polyfunctionalisocyanate curing agents as at least a part of the above curing agents,the curing agents can selectively read with and degrade the functionalgroup-containing monomer having a carboxyl group, and it is thuspossible to adjust the content of the functional group group-containingmonomer having a carboxyl group after curing.

Examples of the polyfunctional isocyanate curing agents may includearomatic polyisocyanate curing agents, aliphatic polyisocyanate curingagents and alicyclic polyisocyanate curing agents. Additionally,aliphatic polyisocyanate curing agents, especially xamethylenediisocyanate curing agent, are preferred. This isocyanate curing agentis preferred for its ability to give flexibility to adhesives and itsefficacy for rugged adherends.

There are no particular restrictions regarding the aromaticpolyisocyanates. Examples may include 1,3-phenylene diisocyanate,4,4′-diphenyl diisocyanate, 1,4-phenylene diisocyanate,4,4′-diphenylmethane diisocyanate, 2,4-tolylene diisocyanate,2,6-tolylene diisocyanate, 4,4′-toluidine diisocyanate,2,4,6-triisocyanate toluene, 1,3,5-triisocyanate benzene, dianisidinediisocyanate, 4,4′-diphenyl ether diisocyanate, 4,4′,4″-triphenylmethanetriisocyanate, ω,ω′-diisocyanate-1,3-dimethyl benzene,ω,ω′-diisocyanate-1,4-dimethyl benzene, ω,ω′-diisocyanate-1,4-diethylbenzene, 1,4-tetramethyl xylylene diisocyanate, and 1,3-tetramethylxylylene diisocyanate.

There are no particular restrictions regarding the aliphaticpolyisocyanates. Examples may include trimethylene diisocyanate,tetramethylene diisocyanate, hexamethylene diisocyanate, pentamethylenediisocyanate, 1,2-propylene diisocyanate, 2,3-butylene diisocyanate,1,3-butylene diisocyanate, dodecamethylene diisocyanate and2,4,4-trimethyl hexamethylene diisocyanate.

There are no particular restrictions regarding the alicyclicpolyisocyanates. Examples may include3-isocyanatomethyl-3,5,5-trimethylcyclohexyl isocyanate,1,3-cyclopentane diisocyanate, 1,3-cyclohexane diisocyanate,1,4-cyclohexane diisocyanate, methyl-2,4-cyclohexane diisocyanate,methyl-2,6-cyclohexane diisocyanate, 4,4′-methylene bis(cyclohexylisocyanate), 1,4-bis(isocyanatomethyl)cyclohexane and1,4-bis(isocyanatomethyl)cyclohexane.

Polyfunctional epoxy curing agents may be basically compounds containingat least two epoxy groups and at least one tertiary nitrogen atom,including N,N-glycidyl aniline, N,N-glycidyl toluidine,m-N,N-glycidylaminophenylglycidylether,p-N,N-glycidylaminophenylglycidylether, triglycidyl isocyanurate,N,N,N′,N′-tetraglycidyldiaminodiphenylmethane,N,N,N′,N′-tetraglycidyl-m-xylylenediamine andN,N,N′,N′,N″-pentaglycidyldiethylenetriamine.

<Adhesive Sheet>

Adhesive sheet 110 of the present embodiment is made by forming adhesivelayer 103 on base material 106. There are no particular restrictionsregarding the method for the formation of adhesive layer 103 on basematerial 106. For example, common coating methods such as comma coating,lip coating, gravure coating, roll coating and screen coating may beused. Adhesive layer 103 may be directly formed on base material 106.Alternatively, adhesive sheet 103 may be formed on the surface ofrelease treated release papers, then transferred to a base material film(base material 106).

The thickness of adhesive layer 103 of the present embodiment ispreferably 3 μm or above, and is more preferably 5 μm or above. When thethickness is above these lower bounds, the irregularities on the circuitsurface of semiconductor wafer 101 can be absorbed, thereby reducing theoccurrence of dimples or cracks on the surface of semiconductor wafer101. On the other hand, the thickness of adhesive layer 103 ispreferably 1000 μm or below, and is more preferably 100 μm or below,because costs can be reduced when the thickness is below these upperbounds.

While there are no particular restrictions regarding the method ofstoring adhesive sheet 110 of the present embodiment, one method is toapply a piece of release sheet or release paper such as polyethylenelaminated paper and release treated plastic film to the adhesive surfaceof adhesive layer 103.

<Method for Manufacturing Electronic Parts>

Adhesive sheet 110 of the present embodiment is used for grinding theback side of a semiconductor wafer. In other words, adhesive sheet 110of the present embodiment can be favorably used for securing an assemblyof semiconductor electronic parts in back-grinding. While there are noparticular restrictions on the work piece of adhesive sheet 110,electronic part assemblies commonly called “works” are preferably used.When used in a back-grinding process, adhesive sheet 110 is adhered tothe circuit surface formed on an electronic part assembly.

Electronic part assemblies may include those having a circuit patternformed on an insulating circuit board (or semiconductor wafer 101).Materials constituting the circuit surface may be Si, SiO₂, Si₃N₄, AlSi,AlSiCu, PI or the like. Semiconductor wafers may include silicon wafers,gallium-arsenide and the like. Among these electronic part assemblies,semiconductor wafer 101 is preferably used.

<Back-Grinding>

The back-grinding process is not particularly restricted as to itsprocedures other than the step of securing adhesive sheet 110 onto thecircuit side of an electronic part assembly and grinding the back sideof the circuit. For example, the process may be preferably carried outwith the following steps shown in FIG. 1.

(1) The first step is to mount and secure an electronic part assembly bysuction onto a mechanical working chuck table so the circuit side of theelectronic part assembly is in contact with adhesive layer 103 ofadhesive sheet 110.

(2) The second step is to cut adhesive sheet 110 along the periphery ofthe electronic part assembly that has its circuit side stuck to adhesivesheet 110.

(3) The third step is to grind the electronic part assembly to a desiredthickness.

(4) The fourth step is to release the suction of the chuck table and toremove the electronic part assembly secured by adhesive sheet 110 fromthe mechanical working table.

(5) The fifth step is to peel adhesive sheet 110 from the electronicpart assembly and to retrieve the electronic part assembly.

One example of the method for peeling adhesive 110 from the electronicpart assembly and retrieving the electronic part assembly is thefollowing method shown in FIG. 1.

(1) The first step is to secure the ground surface side of an electronicpart assembly onto a chuck table by suction.

(2) The second step is to apply an adhesive release film 104, commonlycalled a “release tape”, to adhesive sheet 110.

(3) The third step is to peel off adhesive release film 104. Adhesivesheet 110, which is attached to adhesive release film 104, is peeled offfrom the electronic part assembly.

(4) The fourth step is to release the suction of chuck table 102 and toretrieve the electronic part assembly.

This method is preferably used when the thickness of the insulatingcircuit board (or semiconductor wafer 101) of the electronic partassembly is about 100 μm or above. The electronic part assembly is dicedto yield electronic parts (chips).

When the electronic part assembly (or semiconductor wafer 101) isfragile, adhesive sheet 110 is peeled off from the electronic partassembly (or semiconductor wafer 101) to retrieve the electronic partassembly (or semiconductor wafer 101) by, for example, the followingmethod comprising modifications of the steps shown in FIG. 1.

(1) The first step is to secure the ground surface side of an electronicpart assembly (or semiconductor wafer 101) onto a dicing tape mounted ona mechanical working chuck table (not shown).

(2) The second step is to apply an adhesive release film 104, commonlycalled a “release tape”, to adhesive sheet 110.

(3) The third step is to peel off adhesive release film 104. Adhesivesheet 110, which is attached to adhesive release film 104, is peeled offfrom the electronic part assembly (or semiconductor wafer 101).

This method is preferably used when the insulating circuit board (orsemiconductor wafer 101) of the electronic part assembly is thin andfragile. The electronic part assembly is diced to yield electronicparts.

<Effects>

Herebelow, the effects of the present embodiment shall be described.

Adhesive sheet 110 of the present embodiment comprises a sheet-like basematerial 106 and an adhesive layer 103 laminated on one surface of basematerial 106. Moreover, by keeping the average roughness of one surfaceof base material 106 to at least 0.1 μm and at most 3.5 μm and theaverage roughness of the other surface of base material 106 to at least0.05 μm and at most 0.7 μm in adhesive sheet 110, blocking that occursduring unwinding of rolled adhesive sheet 110 can be reduced, minuteirregularities (waving) that occurs on the surface of groundsemiconductor wafer 101 can be suppressed, and the transparency ofadhesive sheet 110 can further be maintained.

Moreover, at least a part of base material 106 of adhesive sheet 110 ofthe present embodiment preferably comprises ethylene vinyl acetate.Since this embodiment allows the stiffness of base material 106 to beeasily adjusted, the vertical motion of semiconductor wafer 101 causedby impacts from the grinding head (not shown) can be suppressed andsemi-conductor wafer 101 can be easily ground to an even thickness.

Additionally, base material 106 of adhesive sheet 110 of the presentembodiment may be formed of multiple layers, and at least one layeramong the multiple layers may comprise ethylene vinyl acetate. Sincethis embodiment, like the above embodiment, allows the stiffness of basematerial 106 to be easily adjusted, the vertical motion of semiconductorwafer 101 caused by impacts from the grinding head (not shown) can besuppressed and semiconductor wafer 101 can be easily ground to an eventhickness.

Furthermore, the vinyl acetate content of the above ethylene vinylacetate in adhesive sheet 110 of the present embodiment is preferably atleast 3% and at most 20% by mass. Since this embodiment allows stressesacting on adhesive sheet 110 during grinding to be absorbed, cracks inthe ground semiconductor wafer 101 can be reduced. Additionally, sincethis embodiment allows the flexibility of adhesive sheet 110 to beadjusted, the degree of grinding precision of semiconductor wafer 101can be enhanced.

Moreover, adhesive layer 103 of adhesive sheet 110 of the presentembodiment preferably comprises acrylic polymers, because thisconstitution allows the adhesive strength of adhesive layer 103 to beeasily engineered.

Additionally, at least one of the acrylic monomers constituting theabove acrylic polymers is preferably a hydroxyl group-containingmonomer. Since this constitution enhances the adhesive strength ofadhesive layer 103 towards the adherend, water penetration can bereduced.

Furthermore, in adhesive sheet 110 of the present embodiment, thecontent of the above hydroxyl group-containing monomer is preferably atleast 0.01% and at most 10% by mass in the acrylic polymers. Thisconstitution not only enhances the adhesive strength of adhesive layer103 towards the adherend to a degree that water penetration is reduced,it also prevents the adhesive strength of adhesive layer 103 towards theadherend from being overly strong, and so adhesive residues can bereduced.

Moreover, adhesive layer 103 of adhesive sheet 110 of the presentembodiment preferably further comprises curing agents. Since thisconstitution prevents the adhesive strength of adhesive layer 103towards the adherend from being overly strong, adhesive residues can bereduced.

Additionally, adhesive layer 103 of adhesive sheet 110 of the presentembodiment preferably comprises at least 0.1 and at most 20 parts of thecuring agents by mass per 100 parts of the acrylic polymers by mass.This constitution allows the adhesive strength of adhesive layer 103towards the adherend to be adjusted within a moderate range, so adhesiveresidues can be reduced.

Furthermore, after the above acrylic polymers and curing agents reactand cure adhesive layer 103 of adhesive sheet 110 of the presentembodiment, the content of the carboxyl group-containing monomerconstituting the acrylic polymers is preferably 1% or below by mass.Since this constitution prevents the adhesive strength of adhesive layer103 towards metals from being overly strong, adhesive residues can bereduced.

Moreover, at least a part of the above curing agents of adhesive sheet110 of the present embodiment preferably comprises a polyfunctionalisocyanate curing agent. The reason for employing a polyfunctionalisocyanate curing agent is that this curing agent can react withhydroxyl group and carboxyl group-containing monomers and therebydegrade them.

Additionally, the above polyfunctional isocyanate curing agent ofadhesive sheet 110 of the present embodiment is preferably ahexamethylene diisocyanate curing agent. This hexamethylene diisocyanatecuring agent is preferred because of its ability to give flexibility toadhesives and its efficacy for rugged adherends. Moreover, it candestroy hydroxyl and carboxyl groups by reacting with them, and theamount of functional group-containing monomers can be adjusted byparticularly allowing the curing agent to selectively react withhydroxyl group-containing monomers.

Furthermore, at least a part of the above curing agents of adhesivesheet 110 of the present embodiment are preferably polyfunctional epoxycuring agents. Polyfunctional epoxy curing agents can react with bothhydroxyl groups and carboxyl groups to degrade them. Polyfunctionalepoxy curing agents, in particular, can selectively react with carboxylgroup-containing monomers, and therefore the curing agents canselectively degrade these carboxyl groups. The amount of carboxylgroup-containing monomers after curing can thus be adjusted.

Moreover, adhesive sheet 110 of the present embodiment is preferablyused for grinding the back of semiconductor wafers (back-grinding). Thisis because, as described above, adhesive sheet 110 of the presentembodiment can reduce blocking incidences during unwinding of rolledadhesive sheet 110, suppress occurrences of minute irregularities(waving) on the surface of semi-conductor wafer 101 after the back ofthe semiconductor wafer is ground (back-grinding), and can furthermaintain the transparency of adhesive sheet 110.

Additionally, the process for manufacturing an electronic part of thepresent embodiment is a process for manufacturing an electronic part bygrinding semiconductor wafer 101, comprising a step of applyingsemiconductor 101 to the surface of adhesive layer 103 of the aboveadhesive sheet 110 and a step of grinding the exposed surface ofsemiconductor wafer 101 smooth while it is stuck to adhesive sheet 110.

The average surface roughnesses for both surfaces of base material 106of adhesive sheet 110 used in this process are, as described above,adjusted within their specified ranges. For that reason, this processcan reduce blocking incidences during unwinding of rolled adhesive sheet110, suppress occurrences of minute irregularities (waving) on theground surface of semiconductor wafer 101, and can further maintain thetransparency of adhesive sheet 110.

The process for manufacturing an electronic part of the presentembodiment may further comprise a step of peeling adhesive layer 103from semiconductor wafer 101 after the above grinding process. Since theaverage surface roughnesses for both surfaces of base material 106 ofadhesive sheet 110 used in this process are adjusted, blocking thatoccurs during unwinding of rolled adhesive sheet 110 can be reduced,minute irregularities (waving) that occurs on the ground surface ofsemiconductor wafer 101 can be suppressed, and the transparency ofadhesive sheet 110 can further be maintained.

Moreover, this process can prevent blocking incidences during unwindingof rolled adhesive sheet 110, improve the grindability of semiconductorwafer 101 comprising various materials that form a circuit, and furtherprovides the effect of preventing any contamination of a submicronorder. In other words, while back-grinding processes using conventionaladhesive sheets would have resulted in cases where adhesive residues ofa submicron order are left on semiconductor wafer 101 comprising variousmaterials, the present process can solve these problems.

Embodiments of the present invention have been described as above withreference to the drawings. However, they serve only as examples for thepresent invention; various constitutions other than the above may beadopted.

For example, the above embodiments did not place any particularrestrictions on the type of semi-conductor wafer 101. However, any typeof wafer (such as silicon wafers and gallium arsenide wafers) may beused. Since there is a suitable grinding head (not shown) forback-grinding of each type of wafer, processes for manufacturingelectronic parts similar to the above embodiments can be carried outusing suitable grinding heads (not shown), and similar effects may beachieved in such cases.

EXAMPLES

Herebelow, the present invention shall be further explained usingexamples. However, the present invention is not limited to theseexamples.

Example 1

Example 1 shows the recipes for manufacturing the adhesive sheet.

(Base Material)

Ethylene vinyl acetate base material: Commercially available pellets[manufactured by Tosoh Corporation, product name: Ultrasen (Urutorasen)520F] mainly composed of ethylene vinyl acetate containing 8% vinylacetate were dissolved and formed into a film by T-die co-extrusion. Bycontrolling an embossing roller during the formation of the film, theaverage surface roughness (Ra1) of one surface of the base material wasset at 2.0 μm and the average surface roughness (Ra2) of the othersurface of the base material was set at 0.3 μm. Moreover, the thicknessof the film was 120 μm.

(Adhesive)

A synthetic product comprising copolymers obtained by copolymerizing 80%butyl acrylate, 19% methyl(meth)acrylate and 1% 2-hydroxyethyl acrylate(functional group-containing monomer) was obtained. Moreover, the glasstransition point of the synthetic product was −53.3° C.

Additionally, a polyfunctional isocyanate curing agent: hexamethylenediisocyanate (manufactured by Nippon Polyurethane Industry Co., Ltd.,product name: Coronate HL) was further appropriately added to the abovesynthetic product to make an adhesive.

The adhesive was then applied to a PET separator film, coating the filmso that the dried adhesive layer would have a thickness of 20 μm. Theadhesive layer was then laminated onto the 120 μm-thick base materialfilm to obtain an adhesive sheet.

Examples 2-4 and Comparative Examples 1-2

Aside from changing the average surface roughnesses of the base materialsurface not coated with the adhesive (Ra2) to the values shown in Table1, Examples 2-4 and Comparative Examples 1-2 had the same settings asExample 1.

Examples 5-8 and Comparative Examples 3-4

Aside from changing the average surface roughnesses of the base materialsurface coated with the adhesive (Ra1) to the values shown in Table 1,Examples 5-8 and Comparative Examples 3-4 had the same settings asExample 1.

<Method for Evaluation>

(1) Grindability: As shown in FIG. 1, an adhesive sheet 110 was appliedto a 5-inch mirror wafer (semiconductor wafer 101) [FIG. 1( a)], whichwas ground to a thickness of 300 μm [FIG. 1( b)]. The ground surface ofthe mirror wafer (semiconductor wafer 101) was then secured to a vacuumchuck table 102 [FIG. 1( c)] and adhesive sheet 110 was peeled off usinga release film 104 [FIG. 1( d)]. The ground silicon wafer (semiconductorwafer 101) was then evaluated using a flatness measuring apparatus(Flatness Tester; ADE-9500). The results were rated “B” when thedifference between the concavity and convexity on the surface was 5 μmor less; and “C” when it was 5μ or more. Results of the evaluation areshown in Table 1 below.

Mounter: Mounter ATM-1100 manufactured by Takatori CorporationGrinder: Back Grinder DFG-850 manufactured by DISCO Inc.

(2) Blocking: As shown in FIG. 2, after adhesive sheet 110 was made[FIG. 2( a)], it was applied to a release liner 105 [FIG. 2( b)] andwound into a roll [FIG. 2( c)]. Then, the results were rated “A” forthose that did not have any blocking incidences during the unwinding ofthe adhesive sheet [between FIG. 2( c) and FIG. 2( d) (not shown)], “B”for those that had blocking but were still usable and “C” for those thathad blocking and could not be used anymore. Results of the evaluationare shown in Table 1 below.

(3) Transparency: The transparency of the adhesive sheet was evaluatedusing a Haze Meter manufactured by Suga Test Instruments Co., Ltd.(HZ-2). The results were rated “A” for those with 0-20% HAZE, “B” forthose with 20-40% HAZE and “C for those with 40-100% HAZE. Results ofthe evaluation are shown in Table 1 below.

TABLE 1 Co. Co. Co. Co. Ex. 1 Ex. 2 Ex. 3 Ex. 4 Ex. 5 Ex. 6 Ex. 7 Ex. 8Ex. 1 Ex. 2 Ex. 3 Ex. 4 Avg. surface 2.0 2.0 2.0 2.0 0.2 1.0 3.0 3.3 2.02.0  0.08 4.0 roughness Ra1 [μm] Avg. surface 0.3  0.08 0.5 0.6 0.3 0.30.3 0.3  0.03 0.8 0.3 0.3 roughness Ra2 [μm] HAZE [%] A A B B A A A B AC A C Grindability B B B B B B B B B B B C Blocking [—] B A A A B A A AC A C A

<Test Analysis>

As can be seen from the test results shown in the table, adjusting theaverage surface roughness of the two surfaces of the base materialconstituting the present adhesive sheet within their respectivespecified ranges can reduce blocking incidences during the unwinding ofthe rolled adhesive sheet, and suppress occurrences of minuteirregularities (waving) on the ground wafer surface, while allowing thetransparency of the adhesive sheet to be maintained.

While the present invention has been explained using the Examples above,the examples only serve to illustrate the present invention. Variousalternative modifications are possible, and those skilled in the artwill understand that these alternative possibilities are also covered bythe present invention.

INDUSTRIAL APPLICABILITY

The above adhesive tape reduces blocking during the winding of the basematerial, and blocking when put in the form of a tape, and hastransparency. Moreover, the above adhesive tape can be used on variousmaterials forming circuits and provide effects such as grindability andprevention of contamination of a submicron order.

1. An adhesive sheet comprising a sheet-like base material and anadhesive layer laminated on one surface of said base material, whereinone surface of said base material has an average surface roughness of atleast 0.1 μm and at most 3.5 μm and the other surface of said basematerial has an average surface roughness of at least 0.05 μm and atmost 0.7 μm.
 2. The adhesive sheet according to claim 1, wherein atleast a part of said base material comprises ethylene vinyl acetate. 3.The adhesive sheet according to claim 2, wherein said base material isformed of multiple layers and at least one layer of said multiple layerscomprises ethylene vinyl acetate.
 4. The adhesive sheet according toclaim 2, wherein the vinyl acetate content of said ethylene vinylacetate is at least 3% by mass and at most 20% by mass.
 5. The adhesivesheet according to claim 1, wherein said adhesive layer comprises anacrylic polymer.
 6. The adhesive sheet according to claim 5, whereinsaid acrylic polymer comprises acrylic monomers and at least one of saidacrylic monomers is a hydroxyl group-containing monomer.
 7. The adhesivesheet according to claim 6, wherein the content of said hydroxylgroup-containing monomers is at least 0.01% by mass and at most 10% bymass of said acrylic polymer.
 8. The adhesive sheet according to claim5, wherein said adhesive layer further comprises a curing agent.
 9. Theadhesive sheet according to claim 8, wherein said adhesive layercomprises at least 0.1 part and at most 20 parts of said curing agent bymass per 100 parts of said acrylic polymer by mass.
 10. The adhesivesheet according to claim 8, wherein at least a part of said curing agentis a polyfunctional isocyanate curing agent.
 11. The adhesive sheetaccording to claim 10, wherein said polyfunctional isocyanate curingagent is a hexamethylene diisocyanate curing agent.
 12. The adhesivesheet according to claim 8, wherein at least a part of said curing agentis a polyfunctional epoxy curing agent.
 13. The adhesive sheet accordingto claim 8, wherein the content of carboxyl group-containing monomersconstituting said acrylic polymer, after said acrylic polymer is reactedwith said curing agent to cure said adhesive layer, is at most 1% ofsaid acrylic polymer by mass.
 14. The adhesive sheet according to claim1, for use in grinding the back side of a semiconductor wafer.
 15. Aprocess for manufacturing an electronic part, wherein the electronicpart is obtained by grinding a wafer, comprising a step of applying saidwafer to said adhesive layer surface of the adhesive sheet according toclaim 1, and a step of grinding the exposed surface of said wafer smoothwhile keeping said wafer stuck to said adhesive sheet.
 16. The processfor manufacturing an electronic part according to claim 15, furthercomprising a step of peeling said adhesive layer from said wafer aftergrinding.